More evidence supporting the premise that increased vitamin D blood levels results in a decrease in the incidence of breast cancer.

Breast cancer: A study in Carcinogenesis in 2008 found that breast cancer risk was 70% lower in women with blood levels of vitamin D greater than 30 ng/mL compared with those with blood levels less than 18 ng/mL.20 In the Third National Health and Nutrition Examination Survey, women with greater sun exposure had only one-half the incidence of breast cancer compared with those with less sun exposure.

Data from the Harvard Nurses Health Study and the St George’s Hospital Study found that women with the highest blood levels of calcidiol had a reduced risk of breast cancer. There was a clear dose-response relationship in which those with the lowest blood levels (less than 13 ng/mL) had the highest rates of breast cancer, and rates were successively lower as blood levels increased (up to 52 ng/mL). The blood level associated with a 35% reduction in breast cancer risk can be maintained by taking about 2,000 IU of vitamin D3 per day.